Meander line circuit with an interdigital ground plane

ABSTRACT

An improved meander line, slow wave structure comprising a meander line conductor, a continuous dielectric substrate having a raised meander line shaped upper surface portion and a surrounding flat planar surface portion, a conductive ground plane connected to the flat planar substrate surface, said meander line conductor disposed on the upper surface of said raised portion of the substrate. The conductive ground plane is comprised of a plurality of interdigital fingers positioned around the raised portion of the dielectric substrate.

[4 1 Sept. 9, 1975 United States Patent [191 Bates et a1.

[ 4 MEANDER LINE CIRCUIT WITH AN 3,702,413 11/1972 Glance.......................,.........315/35 3,736,534 5/1973 333/31 INTERDIGITAL GROUND PLANE [75] Inventors: Calvin D. Bates, Neptune; Joseph H.

Primary Examiner-James W, Lawrence Assistant Examiner-Marvin Nussbaum Hartley,

Jackson, both of NJ. The United States of America as Attorney, Agent, or FirmNathan Edelberg; Robert P. Gibson; Arthur L. Bowers Assignee:

[57] ABSTRACT An improved meander line, slow wave structure com- [22] Filed:

prising a meander line conductor, a continuous dielectric substrate having a raised meander line sha ped [52] US. 333/31 R; upper surface portion and a surrounding flat planar 333/84 M ortion H01J 23/24; 1-10]? 9/00 to the flat planar substrate surface, said meander line surface p a conductive ground plane connected [51] Int. Cl H03I-I 3/08 conductor disposed on the upper surface of said raised portion of the substrate. The conductive ground plane [58] Field of Search.... 333/31 R, 31 A, 31 C, 84 R, 333/84v M; 315/35 is comprised of a plurality of interdigital fingers positioned around the raised portion of the dielectric substrate.

3,373,382 333/31 R 4 Claims, 1 Drawing Figure MEANDER LINE CIRCUIT WITH INTERDIGITAL GROUND PLANE The invention described-herein may be manufactured and usedby or for the government for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND or THEIINVEN'TION essentially a conductor having an increased effective length between two straight line points, accomplished by providing a circuitous path (usually a zig-zag pattern formed by right angle conductor segments transversely and longitudinally disposed) which in effect increase the time it takes a wave to travel between two straight line points. The use of a so-calle d meander slow wave structure for reducing the velocity of a microwave signal in the two-four gigahertz frequency range iswell known in the art. Such a device islshown in US. Pat. No. 3,736,5 34, issued to Chaffee, which shows a plurality of conductive fingers disposed between adjacent legs of the meander circuit, the meander line' being mounted on a continuous dielectric substrate with a conductive continuous ground plane disposed on the bottom of the device..Thus, a typical meander line circuit is comprised of a conductive ground plane and an intermediarily disposed dielectric material which acts as the meander circuit support, the meander line conductor being mounted on top of the dielectric material. Because the ground plane and the dielectric supporting material are integral and continuous, construction and operational difficulties result from thermal expansions and contractions of different materials, making the conventional device expensive to fabricate. Bandwidth, interaction impedance, and other electrical properties are compromised because of the excessive dielectric loading of devices shown in the prior art.

The instant invention provides distinct advantages over prior art meander line circuits in that it achieves low cost circuit construction, eliminates the need for a large amount of various elements, and has unitary type construction which allows the device to be sprayed, sputtered or deposited to form the interdigital ground plane and the meander line conductor circuit itself. The device is especially useful in microwave circuit elements such as filters, anode circuits for microwave tubes (TWT and crossedfield), and delay lines. The meander line conductive circuit in the instant invention is raised above the ground plane sufficiently to achieve a proper RF match with tube input and output circuits.

BRIEF DESCRIPTION OF THE INVENTTON A meander line, slow wave device comprising a meander shaped conductor, the conductor having a continuous length formed from a plurality of transverse and longitudinal segments coupled together substantially at right angles, the transverse segments disposed substantially on a zig-zag fashion equally about either side of the longitudinal axis of the device, a unitary planar dielectric substrate, said substrate having a raised dielectric meander line shaped portion protruding above one surface, said meander shaped conductor disposed on the upper surface of said raised dielectric substrate portion and a conductive ground plane disposed on the substrate surface in an interdigital fashion adjacent the raised surface portion and below the meander shaped conductor. The eonstruction of .the'device may be achieved by spraying, sputtering or depositing the conductive materials to form the interdigital ground plane and the meander line circuit, the meander line conductor being deposited and bonded on the upper surface of the raised portion of the substrate. RF input and output connectors are coupled to the meander line conductor in a conventional manner.

The conductor ground plane acts essentially as a metallic conductor having an interdigital array of conductive elements spaced below the plane of the meander line circuit conductor. 7 i 7 The dielectric substrate material is determined by the frequency, band-width, and RF power requirements of the device. Beryllia BeO) is the optimum choice in most cases because of low RF loss, moderate dielectric constant and high thermal conductivity.

It is an object of this invention to provide an improved meander line slow wave circuit device of relatively low cost construction.

It is another object of this invention to provide a meander line slow wave device having unitary construcflori- And yet still another object of this invention is to provide an improved meander line circuit device having an interdigital ground plane.

In accordance with these and other objects which will be apparent hereinafter, the instant invention will now be described with particular reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING The drawing shows an exploded, perspective view of the instant invention.

PREFERRED EMBODIMENT OF THE INVENTION Referring now to the drawing, the instant invention is shown generally at 10 comprising a dielectric substrate 12 having bonded to its upper surface a metallic conductive ground plane 14, the ground plane 14 having interdigital fingers l9 and slot 20 exposing dielectric material 12. The slot 20 is formed from a plurality of transverse and longitudinally disposed segments connected at right angles to each other, the longitudinal axis of the ground plane substantially dividing the transverse segments in half. The dielectric substrate, as shown in the exploded view, includes a raised surface protrusion 18 shaped in the form of the meander line conductor 16, which supports the meander line conductor l6 and is bonded thereto. Although shown in the exploded form, the raised protrusion 18 may be formed with the substrate 12 as a unitary body. The conductive ground plane 14 and the meander line conductor 16 are disposed on the substrate 12 and raised protrusion 18 by sputtering, spraying or other depositing technique. The device may also be constructed with segmcntized parts or in the unitary manner described above.

The interdigital ground plane shown in the instant invention allows for unitary construction. The noncomplexity of the device and the thin (0.002 inch or less) conductive surfaces eliminate problems found in the prior art involving thermally caused expansion and contraction of different joined materials.

In operation, conventional RF input and output couplers would be connected to each end of the meander line conductor 16 for proper operation, The conductor 16 is spaced and raised above the surface of the ground plane 14 to provide the proper RF circuit matching and loading for the particular RF signals to be utilized with the device. The device may be utilized in microwave devices as a filter, anode circuit for microwave tubes (TWT and crossed-field), and delay lines. The substrate 12 may also include as optional a pair of internal conduits disposed longitudinally therethrough which may operate as cooling channels.

The instant invention has been shown and described herein in what is considered to be the most practical and preferred embodiment. It is recognized, however, that departures may be made therefrom within the scope of the invention and that obvious modifications will occur to a person skilled in the art.

What is claimed is:

l. A meander line slow wave circuit device comprising:

a unitary dielectric planar support, said dielectric support having a raised surface portion, said raised surface portion being shaped to form a meander line having a plurality of transverse and longitudinal segments disposed at right angles to each other. the transverse segments being substantially sized in length to be equally disposed on either side of the longitudinal axis of said planar support;

a conductive ground plane disposed on the upper surface of said dielectric support adjacent said raised portion of said dielectric to form a continuous planar surface surrounding said raised dielectric portion; and

a conductor disposed on the upper surface portion of said raised dielectric portion.

2. A meander slow wave device, as in claim 1,

wherein:

said upper meander conductor is bonded to the upper surface of said raised dielectric surface portion, said conductor being separated from said ground plane a sufficient distance to provide proper RF signal matching.

3. A meander line slow wave device, as in claim 2, including: RF signal input and output means connected to the meander line conductor.

4. A meander line slow wave structure comprising:

a planar shaped dielectric substrate;

a dielectric meander shaped structure disposed on and protruding above the upper surface of said dielectric substrate;

a meander line conductor mounted on the upper surface of said dielectric meander line structure; and

a conductive ground plane mounted on the upper surface of said planar shaped dielectric substrate, said conductive ground plane having interdigital fingers extending about said dielectric meander shaped structure. 

1. A meander line slow wave circuit device comprising: a unitary dielectric planar support, said dielectric support having a raised surface portion, said raised surface portion being shaped to form a meander line having a plurality of transverse and longitudinal segments disposed at right angles to each other, the transverse segments being substantially sized in length to be equally disposed on either side of the longitudinal axis of said planar support; a conductive ground plane disposed on the upper surface of said dielectric support adjacent said raised portion of said dielectric to form a continuous planar surface surrounding said raised dielectric portion; and a conductor disposed on the upper surface portion of said raised dielectric portion.
 2. A meander slow wave device, as in claim 1, wherein: said upper meander conductor is bonded to the upper surface of said raised dielectric surface portion, said conductor being separated from said ground plane a sufficient distance to provide proper RF signal matching.
 3. A meander line slow wave device, as in claim 2, including: RF signal input and output means connected to the meander line conductor.
 4. A meander line slow wave structure comprising: a planar shaped dielectric substrate; a dielectric meander shaped structure disposed on and protruding above the upper surface of said dielectric substrate; a meander line conductor mounted on the upper surface of said dielectric meander line structure; and a conductive ground plane mounted on the upper surface of said planar shaped dielectric substrate, said conductive ground plane having interdigital fingers extending about said dielectric meander shaped structure. 